Conventionally, there is an image forming apparatus having a decoloring mode in which an image formed on paper is decolored. For example, the image forming apparatus heats the paper on which the image is printed with decolorable toner at a constant temperature to decolor the image. In this way, the image forming apparatus can make the paper printed with the decolorable toner reusable.
During the decoloring processing, each device in the image forming apparatus is controlled and the paper-passing is performed, similar to that during the general image forming processing. During the decoloring processing, the temperature of a fixing device is set to the decoloring temperature of toner to heat the paper.
The paper, on which the toner is fixed, has a high chargeability. This interferes with the conveyance of paper in the decolorizing process. Thus, it is considered to set, during the decoloring processing, the absolute value of a transfer bias voltage to be applied to a transfer device to 0 or a value smaller than that at the time of an image formation. However, when setting the absolute value of the transfer bias voltage to 0 or a value smaller than that at the time of the image formation, the following problems may occur.
The image forming apparatus using two-component developer controls the applying timing or terminating timing of a charging bias voltage and a developing bias voltage when the image forming processing is started and the image forming processing is ended. Through these control process, a carrier constituting the developer can be prevented from being adhered to a photoconductor. At this time, a small quantity of toner adheres to the photoconductor. Thus, if the absolute value of the transfer bias voltage is set to 0 or a smaller value during the decoloring processing, the toner adhered to the photoconductor may be adhered to the transfer device, which will stain the paper.